The utilization of electric machines in drive trains of vehicles, in particular in motor vehicles, is already known. They can fulfill multiple functions, such as, for example, drive units in hybrid systems, auxiliary drives for all-wheel drives, gear drives for the realization of reverse gears, starter motors for internal combustion engines, starting aids, electrodynamic retarders, and pump drives for lubricating and cooling the oil supply or generators in recuperation devices. It is also known how to use electric machines for synchronization in manual transmissions, in order to be able dispense, at least in part, with the conventional synchronization devices with friction elements to obtain savings in productions costs and installation space, shorten the response times, and improve the shift comfort.
A drive train of such a motor vehicle as well as a method for its operation is known from DE 10 2005 007 966 A1. In it an electric motor is provided in a drive train arrangement in the force flow direction which consists of a combustion engine —engine clutch—electric motor—input shaft—manual transmission/manual transmission—axle transmission that can be used, among other things, for the synchronization of gear shifting in manual transmissions, whereby the electric motor brings about, for example, a synchronization speed between the transmission shaft and the gear wheel to be engaged before the respectively selected target gear is shifted. Also mentioned in this publication is that synchronization by means of an electric motor can be accomplished by several repeated productions of a synchronous speed in unsynchronized multigroup transmissions. A more detailed description of this is not found, however, in this publication.
The use of electric machines is also known in dual clutch transmissions. Described in the unpublished DE 10 2006 036 758.8 of the applicant is an automated dual clutch transmission in a countershaft transmission design having two transmission input shafts to which are allocated a group of gear wheel sets and a starting element, respectively, as well as shift elements configured as unsynchronized gear clutches. The two starting elements configured as dual clutch units are configured as unsynchronized engine clutches in a claw design. They are connected on the side of the transmission with an associated input shaft and can be alternatively connected on the input side to the crankshaft of an internal combustion engine. Either an electric machine whose rotor is engaged via a pinion gear to the fixed wheel of the highest gear of the respective gear group or a common electric machine which can alternatively be actively connected to the gear wheels, is associated with the two input shafts
The electric machine acts as a starting and synchronization means. After the gear clutch of the starting gear of the vehicle is engaged by means of the electric machine during the starting operation, it is first accelerated until a synchronous speed of the input shaft has been reached at which the corresponding engine clutch can be engaged. During a gear change the input shaft of the target gear is first accelerated by means of the associated electric machine with the engine clutch of the target gear disengaged, until the gear clutch of the target gear can be engaged when a synchronous speed is reached, whereupon the electric machine temporarily absorbs the load that has built up until the engine clutch has disengaged the original gear, the original gear has been released, and the drive engine is controlled by a control mechanism to the new synchronous speed, so that the engine clutch of the target gear can then be engaged. Furthermore, a reverse gear can be realized by reversing the direction of rotation of the rotor of the electric machine of the at least one electric machine actively connected with a gear wheel set for a forward starting gear.
Known from DE 101 33 695 A1 is a dual clutch transmission in which at least one transmission input shaft can be connected to an electric machine. An acceleration can be achieved during a gear shift by means of the electric machine for a synchronization of the transmission input shaft or a speed reduction can be achieved by shifting down into the lowest gear. The electric machine can interact therein with the available synchronization devices.
The mentioned publications disclose a multitude of utilization possibilities for electric machines in vehicle drive trains, in particular for synchronization in conventional manual transmissions and dual clutch transmissions, and are able to fulfill their basic tasks to their full extent. It is disadvantageous, that the person skilled in the art can find no, or at least only insufficient, instructions concerning the mode of operation for the application of electric machines in problematic and/or comparatively complex gear shifts.